Drive unit

ABSTRACT

A drive unit includes an ultrasonic actuator having an actuator body formed using a piezoelectric element, and a driving element provided on the actuator body and configured to output a driving force by moving according to the vibration of the actuator body, and a control section configured to induce the vibration in the actuator body by applying a first and a second AC voltages having a same frequency and different phases to the piezoelectric element. The control section adjusts the first AC voltage and the second AC voltage so that the first AC voltage and the second AC voltage have different voltage values from each other.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2009-027879 filed on Feb. 9, 2009, the disclosure of which including thespecification, the drawings, and the claims is hereby incorporated byreference in its entirety.

BACKGROUND

1. Technical Field

The technology disclosed herein relates to a drive unit including avibratory actuator having an actuator body and driver elements.

2. Background Art

Drive units including vibratory actuators for use in various electricdevices have been conventionally known (e.g., Japanese PatentPublication No. 2008-193874).

A vibratory actuator associated with a drive unit described in JapanesePatent Publication No. 2008-193874 includes an actuator body configuredwith a piezoelectric element, and a driver element provided on theactuator body is disposed so as to contact a rotor, which is a movableelement. This drive unit induces vibration in the actuator body byapplying two alternating current (AC) voltages having a same frequencyand different phases to the piezoelectric element in the actuator body,thereby causing the driver element to move accordingly. In doing so, adriving force is transmitted from the driver element to the rotor, andthus the rotor is driven in a predetermined direction. In this regard,the drive unit controls the rotation speed of the rotor by adjusting thephase difference between the two AC voltages depending on the deviationbetween a target and an actual rotation speeds of the rotor.

SUMMARY

However, since a piezoelectric element has a piezoelectric effect, theinput voltage of one channel and the input voltage of the other channelhave interaction with each other. In addition, the ratio in theinteraction may be non-uniform due to asymmetry introduced in amanufacturing process of elements and due to asymmetry of distributionof pressure applied to an element in driving operation. In such a case,the amounts of currents which flow may differ from each other dependingon the frequencies or the phase difference of the two AC voltages evenif same AC voltages are applied, which may cause a current exceeding thescope of the assumption to flow, thus the power consumption mayincrease.

The technology disclosed herein has been developed in view of theforegoing, and it is an object of the technology to provide a drive unitwith low power consumption.

A drive unit disclosed herein includes a vibratory actuator having anactuator body formed using a piezoelectric element, and configured tooutput a driving force by inducing vibration in the actuator body, and acontrol section configured to induce the vibration in the actuator bodyby applying a first and a second AC voltages having a same frequency anddifferent phases to the piezoelectric element, where the control sectionadjusts the first AC voltage and the second AC voltage so that the firstAC voltage and the second AC voltage have different voltage values fromeach other.

According to the drive unit, the voltage values of the two AC voltagesapplied to the actuator body can be different from each other ratherthan constantly coincident, and thus the voltage value of either of theAC voltages can be adjusted depending on an operational condition,thereby allowing a reduction of the power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a drive unit according to anembodiment of the present disclosure.

FIG. 2 is a perspective view of the drive unit.

FIG. 3 is a developed view of an actuator body by orthographicprojection.

FIGS. 4A-4D are diagrams illustrating respective layers of the actuatorbody as viewed from the stacking direction.

FIG. 5 is a diagram for illustrating four regions on a principal face ofthe actuator body.

FIG. 6 is a diagram illustrating positional relationships of connectionbetween flexible cables and the side faces of the actuator body.

FIG. 7 is a circuit diagram of an ultrasonic actuator and a drive powersupply.

FIG. 8 is a conceptual diagram illustrating a deviation in stretchingvibration of a first-order mode of the ultrasonic actuator.

FIG. 9 is a conceptual diagram illustrating deviations in bendingvibration of a second-order mode of the ultrasonic actuator.

FIGS. 10A-10D are conceptual diagrams illustrating a motion of theultrasonic actuator.

FIGS. 11A-11B are graphs showing a first and a second drive voltages anda first and a second currents corresponding to respective ones when thecurrent values of the first and the second currents are generally thesame; FIG. 11A shows the drive voltages, and FIG. 11B shows thecurrents.

FIGS. 12A-12B are graphs showing a first and a second drive voltages anda first and a second currents corresponding to respective ones when thecurrent values of the first and the second currents are significantlydifferent from each other; FIG. 12A shows the drive voltages, and FIG.12B shows the currents.

FIGS. 13A-13B are graphs showing a first and a second drive voltages anda first and a second currents corresponding to respective ones when thecurrent values of the first and the second currents are made generallythe same by adjusting the first drive voltage to a lower value; FIG. 13Ashows the drive voltages, and FIG. 13B shows the currents.

FIGS. 14A-14B are graphs showing a first and a second drive voltages anda first and a second currents corresponding to respective ones when thecurrent values of the first and the second currents are made generallythe same by adjusting the second drive voltage to a higher value; FIG.14A shows the drive voltages, and FIG. 14B shows the currents.

FIGS. 15A-15B are graphs showing a first and a second drive voltages anda first and a second currents corresponding to respective ones when thecurrent value of the first current exceeds an upper limit; FIG. 15Ashows the drive voltages, and FIG. 15B shows the currents.

FIGS. 16A-16B are graphs showing a first and a second drive voltages anda first and a second currents corresponding to respective ones when thecurrent value of the first current is adjusted to less than or equal toan upper limit by adjusting the first drive voltage to a lower value;FIG. 16A shows the drive voltages, and FIG. 16B shows the currents.

FIGS. 17A-17B are graphs showing a first and a second drive voltages anda first and a second currents corresponding to respective ones when thefirst drive voltage is adjusted to a higher value; FIG. 17A shows thedrive voltages, and FIG. 17B shows the currents.

FIGS. 18A-18B are graphs showing square-wave voltages output from afirst and a second amplifier sections; FIG. 18A shows a case beforeadjustment, and FIG. 18B shows a case after adjusting a duty cycle.

FIG. 19 is a perspective view of a drive unit according to anotherembodiment.

FIG. 20 is a perspective view of a drive unit according to still anotherembodiment.

DETAILED DESCRIPTION

Example embodiments of the present invention will be described below indetail with reference to the drawings.

FIG. 1 is a block diagram of a drive unit according to this embodiment,and FIG. 2 is a schematic perspective view of the drive unit. The driveunit 1 according to this embodiment includes an ultrasonic actuator 2, amovable body 9 which is driven by the ultrasonic actuator 2 in apredetermined movable direction, a drive power supply 11 which applies avoltage to the ultrasonic actuator 2, a first and a second currentdetectors 12A and 12B which detect current flowing into the ultrasonicactuator 2, a position sensor 13 which detects the position of themovable body 9, and a control section 10 which controls the ultrasonicactuator 2 by controlling the drive power supply 11.

<<1: Configuration of Ultrasonic Actuator>>

<1.1: Overall Configuration>

The ultrasonic actuator 2 according to this embodiment includes anactuator body 4, driver elements 8 provided on the actuator body 4, acase 5 which houses the actuator body 4, support members 6A-6C whichsupport the actuator body 4 with respect to the case 5, and a first anda second flexible cables 7A and 7B for supplying power to the actuatorbody 4; and the ultrasonic actuator 2 generates a relative driving forcewith respect to the movable body 9 by inducing stretching vibration andbending vibration in the actuator body 4. This ultrasonic actuator 2constitutes a vibratory actuator, and the movable body 9 constitutes adriven object.

As shown in FIG. 2, the actuator body 4 is formed of a piezoelectricelement having a generally rectangular parallelepiped shape (e.g., 6.0mm long, 1.7 mm wide, and 2.0 mm thick). The actuator body 4 has aconfiguration in which piezoelectric element layers and electrode layersare stacked in a direction into the paper of FIG. 2. In FIG. 2, thesurface on the front side of the actuator body 4 as viewed into thepaper is a principal face of a piezoelectric element layer 41. In therest of the document, a pair of principal faces facing each other of apiezoelectric element layer 41 are referred to as “principal faces.” Apair of surfaces facing each other, orthogonal to the principal faces,and parallel to the long sides of the principal faces are referred to as“longer side faces.” A pair of surfaces facing each other, orthogonal tothe principal faces, and parallel to the short sides of the principalfaces are referred to as “shorter side faces.” The principal faces, thelonger side faces, and the shorter side faces constitute the externalsurface of the actuator body 4, and the longer side faces and theshorter side faces constitute the peripheral surface of the actuatorbody 4. In this embodiment, the principal faces have the largest areasof the principal faces, the longer side faces, and the shorter sidefaces. In this embodiment, the actuator body 4 constitutes a vibrator.

The actuator body 4 is housed in the case 5, which is a support. Theactuator body 4 is supported with respect to the case 5 via threesupport members 6A, 6B, and 6C. The three support members 6A, 6B, and 6Care all elastic. The support members 6A and 6C are respectivelypress-fitted between the two shorter side faces and the case 5. In thisway, the actuator body 4 is supported by the support members 6A and 6Cfrom the direction along the long sides of the principal faces.

The first and the second flexible cables 7A and 7B are respectivelyinterposed between the two shorter side faces of the actuator body 4 andthe support members 6A and 6C.

The driver elements 8 are provided on one of the longer side faces ofthe actuator body 4, and the driver elements 8 contact the plate-likemovable body 9. Specifically, the driver elements 8 are fixed nearantinodes of bending vibration of a second-order mode (described later)of the actuator body 4. The driver elements 8 each has a cylindricalshape and makes line contact with the actuator body 4. The driverelements 8 are fixed to the actuator body 4 by adhesive agent. Theadhesive agent used is softer than the piezoelectric element layers 41and the driver elements 8. The softness can be compared in terms of, forexample, modulus of elasticity. The driver elements 8 and the part ofthe movable body 9 which contacts the driver elements 8 are made of, forexample, a ceramic material made primarily of zirconia, alumina, andsilicon nitride, or a resin material.

The support member 6B is provided between the other one of the longerside faces of the actuator body 4, in other words, the longer side faceopposite the longer side face on which the driver elements 8 areprovided, and the case 5. The support member 6B is provided incompression in a direction toward the movable body 9 (i.e., the lateraldirection of the actuator body 4). The support member 6B presses theactuator body 4 against the movable body 9 by its reaction force. Thisincreases the friction forces between the top portions of the driverelements 8 and the movable body 9, and thus the driving force byvibration of the actuator body 4 is efficiently transmitted to themovable body 9 through the driver elements 8.

<1.2: Actuator Body 4>

The actuator body 4 according to this embodiment has a generallyrectangular parallelepiped shape. This actuator body 4 includes aplurality of piezoelectric element layers 41 which are piezoelectricbodies and have generally rectangular shapes, and internal electrodelayers respectively interposed between corresponding pairs of thepiezoelectric element layers 41. The actuator body 4 has a configurationin which the piezoelectric element layers and the electrode layers arestacked in a direction into the paper of FIG. 2 (also referred tohereinafter as thickness direction).

FIG. 3 is a developed view by orthographic projection of the actuatorbody 4 according to this embodiment. In FIG. 3, the center figure is afigure of a principal face; the figures on the both sides thereof arefigures of the shorter side faces; and the figures above and below thefigure of a principal face are figures of the longer side faces.Although the internal electrode layers cannot be seen through thisprincipal face, the positions projected onto the principal face areindicated by dashed lines on the principal face. FIGS. 4A-4D arediagrams illustrating respective layers of the actuator body 4 accordingto this embodiment as viewed in the stacking direction.

As shown in FIG. 4, the actuator body 4 has a generally rectangularparallelepiped shape formed by alternately stacking the piezoelectricelement layers 41, which have generally rectangular shapes, and theinternal electrode layers. The piezoelectric element layers 41 areinsulator layers formed of, for example, a ceramic material such as leadzirconate titanate. The internal electrode layers are formed ofpower-supply electrodes 42 and counter electrodes 43, which are arrangedalternately in the stacking direction (i.e., thickness direction of theactuator body 4) interposing the corresponding piezoelectric elementlayers 41. The internal electrode layers are electrode layers made of,for example, metal made primarily of silver and palladium, and areprovided on the corresponding principal faces of the piezoelectricelement layers 41.

As shown in FIG. 3, an external power-supply electrode 44 and externalcounter electrodes 45 are formed on the shorter side faces of theactuator body 4. More specifically, the external power-supply electrode44 is a combination of a first and a second external power-supplyelectrodes 44A and 44B. The first and the second external power-supplyelectrodes 44A and 44B are provided on one of the two shorter side facesof the actuator body 4. In addition, two external counter electrodes 45are formed, and both are provided on the other shorter side face. Theelectrodes 44A, 44B, and 45 are electrically insulated from each other.In other words, the electrodes 44A, 44B, and 45 are not electricallyconnected together. In addition, a first external connection electrode46A is provided on one of the longer side faces of the actuator body 4,and a second external connection electrode 46B is provided on the otherone of the longer side faces. The first and the second externalconnection electrodes 46A and 46B are electrically insulated from eachother.

As shown in FIGS. 4B and 4C, the power-supply electrodes 42 are providedon a principal face of at least one piezoelectric element layer 41 ofthe plurality of the piezoelectric element layers 41. Specifically, apower-supply electrode 42 is provided on a principal face of at leastone piezoelectric element layer 41 of the plurality of the piezoelectricelement layers 41 in a first pattern as shown in FIG. 4B. In addition,another power-supply electrode 42 is provided on a principal face of adifferent piezoelectric element layer 41 than the piezoelectric elementlayer 41 on which the power-supply electrode 42 is provided in the firstpattern, in a second pattern different from the first pattern as shownin FIG. 4C.

Specifically, the power-supply electrode 42 formed in the first patternand the power-supply electrode 42 formed in the second pattern eachincludes first power-supply electrodes 42A and second power-supplyelectrodes 42B, which are not electrically connected to the firstpower-supply electrodes 42A.

In either pattern of the first and the second patterns, of four regionsA1-A4 (see FIG. 5) made by dividing a principal face of a piezoelectricelement layer 41 into halves respectively in the longitudinal directionthereof L and in the lateral direction thereof S, the first power-supplyelectrodes 42A are formed in the two regions A2 and A4 arranged in afirst diagonal direction D1 of the principal faces of the piezoelectricelement layers 41. In addition, the second power-supply electrodes 42Bare formed in the two regions A1 and A3 arranged in a second diagonaldirection D2 of the principal faces of the piezoelectric element layers41, of the four regions A1-A4 (see FIG. 5).

Furthermore, the power-supply electrode 42 in the first pattern includesa first connection electrode J1 extending in the lateral direction in acenter portion in the longitudinal direction of the correspondingprincipal face of the piezoelectric element layer 41. The firstpower-supply electrodes 42A formed in the two regions A2 and A4 in thefirst pattern are electrically connected together by the firstconnection electrode J1. The power-supply electrode in the secondpattern includes a second connection electrode J2 extending in thelateral direction in a center portion in the longitudinal direction ofthe corresponding principal face of the piezoelectric element layer 41.The second power-supply electrodes 42B formed in the two regions A1 andA3 in the second pattern are electrically connected together by thesecond connection electrode J2.

In addition, in either pattern of the first and the second patterns, afirst power-extraction electrode 42 a extending to the first externalpower-supply electrode 44A is provided on the first power-supplyelectrode 42A formed in the region A2, close to the shorter side facewhere the first external power-supply electrode 44A is formed, of thefirst power-supply electrodes 42A formed in the two regions A2 and A4.Thus, the first power-supply electrode 42A in the region A2 iselectrically connected to the first external power-supply electrode 44Athrough the first power-extraction electrode 42 a. Meanwhile, anotherfirst power-extraction electrode 42 a extending to the first externalconnection electrode 46A formed on a longer side face is provided on thefirst power-supply electrode 42A formed in the region A4, apart from theshorter side face where the first external power-supply electrode 44A isformed, of the first power-supply electrodes 42A formed in the tworegions A2 and A4. In this way, the first power-supply electrodes 42A inthe region A4 provided in different piezoelectric element layers 41 areelectrically connected together through the first external connectionelectrode 46A. In addition, since the first power-supply electrode 42Ain the region A4 of the first pattern is electrically connected to thefirst power-supply electrode 42A in the region A2 through the firstconnection electrode J1, the first power-supply electrode 42A in theregion A4 of the second pattern electrically connected to the firstpower-supply electrode 42A in the region A4 of the first pattern throughthe first external connection electrode 46A is electrically connected tothe first external power-supply electrode 44A through the firstconnection electrode J1 of the first pattern.

Furthermore, in either pattern of the first and the second patterns, asecond power-extraction electrode 42 b extending to the second externalpower-supply electrode 44B is provided on the second power-supplyelectrode 42B formed in the region A3, close to the shorter side facewhere the second external power-supply electrode 44B is formed, of thesecond power-supply electrodes 42B formed in the two regions A1 and A3.Thus, the second power-supply electrode 42B in the region A3 iselectrically connected to the second external power-supply electrode 44Bthrough the second power-extraction electrode 42 b. Meanwhile, anothersecond power-extraction electrode 42 b extending to the second externalconnection electrode 46B formed on a longer side face is provided on thesecond power-supply electrode 42B formed in the region A1, apart fromthe shorter side face where the second external power-supply electrode44B is formed, of the second power-supply electrodes 42B formed in thetwo regions A1 and A3. In this way, the second power-supply electrodes42B in the region A1 provided in different piezoelectric element layers41 are electrically connected together through the second externalconnection electrode 46B. In addition, since the second power-supplyelectrode 42B in the region A1 of the second pattern is electricallyconnected to the second power-supply electrode 42B in the region A3through the second connection electrode J2, the second power-supplyelectrode 42B in the region A1 of the first pattern electricallyconnected to the second power-supply electrode 42B in the region A1 ofthe second pattern through the second external connection electrode 46Bis electrically connected to the second external power-supply electrode44B through the second connection electrode J2 of the second pattern.

As shown in FIG. 4D, the counter electrodes 43 are each provided overmost of the surface of a principal face of the correspondingpiezoelectric element layer 41. Specifically, each of the counterelectrodes 43 is not formed in a peripheral area of the correspondingpiezoelectric element layer 41, but is formed over most of the areainside the peripheral area. The counter electrodes 43 each includescounter extraction electrodes 43 g each extending from either end of theshort side close to the shorter side face where the external counterelectrodes 45 are formed to the external counter electrodes 45, andconnected to the external counter electrodes 45. Thus, each of thecounter electrodes 43 is electrically connected to the external counterelectrodes 45 through the counter extraction electrodes 43 g. Inaddition, the counter electrodes 43 on different piezoelectric elementlayers 41 are electrically connected together through the counterextraction electrodes 43 g and the external counter electrodes 45.

The actuator body 4 is configured by stacking the piezoelectric elementlayers 41 where the power-supply electrodes 42 or the counter electrodes43 configured as described above are provided on principal faces.Specifically, a plurality of piezoelectric element layers 41 are stackedin an order of a piezoelectric element layer 41 on which thepower-supply electrode 42 in the first pattern is provided, apiezoelectric element layer 41 on which the counter electrode 43 isprovided, a piezoelectric element layer 41 on which the power-supplyelectrode 42 in the second pattern is provided, a piezoelectric elementlayer 41 on which the counter electrode 43 is provided, a piezoelectricelement layer 41 on which the power-supply electrode 42 in the firstpattern is provided, a piezoelectric element layer 41 on which thecounter electrode 43 is provided, . . . . In this regard, thepiezoelectric element layers 41 are stacked such that the principalfaces on which the power-supply electrodes 42 or the counter electrodes43 are provided face the same direction, that is, the principal face ofone piezoelectric element layer 41 where one of the power-supplyelectrodes 42 or one of the counter electrodes 43 is provided faces tothe principal face of another piezoelectric element layer 41 on whichneither the power-supply electrodes 42 nor the counter electrodes 43 areprovided. Note that, in order that neither the power-supply electrodes42 nor the counter electrodes 43 may be exposed to the outside, thepiezoelectric element layers 41 on which neither the power-supplyelectrodes 42 nor the counter electrodes 43 are provided are stacked atthe top and/or the bottom of the stack.

As described above, as a result of stacking the piezoelectric elementlayers 41, the power-supply electrodes 42, and the counter electrodes43, each of the piezoelectric element layers 41 is interposed betweenthe corresponding power-supply electrode 42 (more specifically, thefirst and the second power-supply electrodes 42A and 42B) and thecorresponding counter electrode 43. That is, the power-supply electrodes42 and the counter electrodes 43 overlap each other, with thepiezoelectric element layers 41 interposed, as viewed in the stackingdirection. In this regard, each of the piezoelectric element layers 41is polarized in a direction from the power-supply electrode 42 to thecounter electrode 43.

However, there are areas, in the piezoelectric element layers 41, wherethe power-supply electrodes 42 and the counter electrodes 43 do notoverlap each other as viewed in the stacking direction (see FIG. 3). Forexample, the first and the second power-extraction electrodes 42 a and42 b, and the counter extraction electrodes 43 g do not overlap thecounter electrodes 43 and the power-supply electrodes 42, respectively,as viewed in the stacking direction. No electric field is created in theportions of the piezoelectric element layers 41 corresponding to suchareas. That is, such areas are piezoelectrically inactive areas.Specifically, the power-supply electrodes 42 and the counter electrodes43 do not overlap each other as viewed in the stacking direction inareas near the shorter side faces of the piezoelectric element layers41, and thus such areas are piezoelectrically inactive areas.

<1.3: Electrical Connection Members>

In this embodiment, flexible cables are used as electrical connectionmembers. As shown in FIG. 2, the first and the second flexible cables 7Aand 7B are electrically connected to the actuator body 4 on the bothshorter side faces of the actuator body 4. The first and the secondflexible cables 7A and 7B have a same shape.

FIG. 6 is a diagram illustrating positional relationships of connectionbetween the first and the second flexible cables 7A and 7B and the sidefaces of the actuator body 4. As shown in FIG. 6, the first and thesecond flexible cables 7A and 7B include an insulative resin substrateand a plurality of electric wires formed by printing copper on the resinsubstrate. The electric wires are electrically insulated from eachother.

The first flexible cable 7A is connected to one of the shorter sidefaces of the actuator body 4. The first flexible cable 7A includes anelectric wire 51A connected to the first external power-supply electrode44A, and an electric wire 51B connected to the second externalpower-supply electrode 44B.

Meanwhile, the second flexible cable 7B is connected to the other one ofthe shorter side faces of the actuator body 4. The second flexible cable7B includes electric wires 52 connected to the external counterelectrodes 45.

In addition, the first flexible cable 7A has a shape symmetrical about aplane passing through the midpoint of the short side of the principalface of the piezoelectric element layer 41, and orthogonal to the shortside face. Similarly to the first flexible cable 7A, the second flexiblecable 7B also has a shape symmetrical about a plane passing through themidpoint of the short side of the principal face of the piezoelectricelement layer 41, and orthogonal to the short side face. Moreover, thefirst and the second flexible cables 7A and 7B have a configurationsymmetrical about a plane passing through the midpoint of the long sidesof the principal face of the piezoelectric element layer 41, andorthogonal to the principal face.

That is, a connecting portion of the first flexible cable 7A to theactuator body 4 has a shape symmetrical about a plane passing throughthe midpoint of the short side of the principal face of thepiezoelectric element layer 41, and orthogonal to the short side face.Similarly, a connecting portion of the second flexible cable 7B to theactuator body 4 has a shape symmetrical about a plane passing throughthe midpoint of the short side of the principal face of thepiezoelectric element layer 41, and orthogonal to the short side face.Moreover, the connecting portion of first flexible cable 7A to theactuator body 4 and the connecting portion of the second flexible cable7B to the actuator body 4 have a configuration symmetrical about a planepassing through the midpoint of the long sides of the principal face ofthe piezoelectric element layer 41, and orthogonal to the principalface.

Each of the connecting portions between the first and the secondflexible cables 7A and 7B and the actuator body 4 is electricallyconnected and adhered using an anisotropic conductive adhesive film. Theanisotropic conductive adhesive film is made in such a way thatconductive particles are dispersed in resin and the resultant resin ismolded into the form of a film. In addition, the anisotropic conductiveadhesive film is electrically conductive in the adhesion direction, thatis, the thickness direction of the film, but is not electricallyconductive in the directions within the adhesion plane. This allows theplurality of electrodes provided on each shorter side face of theactuator body 4 to conduct electricity to each of the electric wires ofthe first or the second flexible cable 7A or 7B, and to be electricallyinsulated from each other, by one anisotropic conductive adhesive film.The connection procedure is as follows: first, an anisotropic conductivefilm is interposed between the first or the second flexible cable 7A or7B made of polyimide and the actuator body 4. Then, the first or thesecond flexible cable 7A or 7B is pressed towards the actuator body 4using a heated flat iron. This causes the first or the second flexiblecable 7A or 7B and the actuator body 4 to be electrically connected byconductive particles and to be adhered due to the effect of resin of theanisotropic conductive film.

The connecting portions between the first and the second flexible cables7A and 7B and the actuator body 4 are respectively located between thesupport members 6A and 6C and the actuator body 4. That is, the firstflexible cables 7A is pressed to the actuator body 4 by the supportmember 6A. The second flexible cable 7B is pressed to the actuator body4 by the support member 6C.

Note that the electric wire 51A connected to the first externalpower-supply electrode 44A is an example of a first power-supplyconductive member. The electric wire 51B connected to the secondexternal power-supply electrode 44B is an example of a secondpower-supply conductive member. The electric wires 52 connected to theexternal counter electrodes 45 are an example of counter conductivemembers. The first flexible cable 7A is an example of a first electricalconnection member. The second flexible cable 7B is an example of asecond electrical connection member.

The first and the second flexible cables 7A and 7B are connected to thedrive power supply 11 (described later). Applying a drive voltage fromthe drive power supply 11 through the first and the second flexiblecables 7A and 7B to the actuator body 4 causes vibration includingstretching vibration and bending vibration in the actuator body 4. Then,the vibration of the actuator body 4 causes the driver elements 8 tomove in orbital paths according to the movement of the actuator body 4.

<<2: Configuration of Drive Unit>>

The drive power supply 11 in the drive unit 1 includes a clockgeneration section 14, a phase shift section 15, a first and a secondamplifier sections 16A and 16B, a first and a second wave-shapingsections 17A and 17B, and applies a two-phase sinusoidal drive voltageto the actuator body 4.

The clock generation section 14 outputs a square-wave signal (referredto hereinafter as reference clock signal) having a predeterminedreference frequency to the first amplifier section 16A and to the phaseshift section 15 according to a control signal from the control section10. The phase shift section 15 shifts the phase of the reference clocksignal according to the control signal from the control section 10, andoutputs the phase-shifted signal to the second amplifier section 16B.The first and the second amplifier sections 16A and 16B respectivelyamplify the input reference clock signals to a predetermined voltage andoutput the amplified signals to the first and the second wave-shapingsections 17A and 17B. The first and the second wave-shaping sections 17Aand 17B respectively reshape the signals input from the first and thesecond amplifier sections 16A and 16B to sinusoidal waves and output thereshaped signals to the actuator body 4 as a first and a second drivevoltages. The first drive voltage output from the first wave-shapingsection 17A is applied to a portion between the first power-supplyelectrodes 42A and the counter electrodes 43 of the actuator body 4, andthe second drive voltage output from the second wave-shaping section 17Bis applied to a portion between the second power-supply electrodes 42Band the counter electrodes 43 of the actuator body 4.

FIG. 7 is an equivalent circuit diagram of the ultrasonic actuator 2 andthe drive power supply 11. Note that the clock generation section 14 andthe phase shift section 15 are omitted.

The first and the second amplifier sections 16A and 16B are eachconfigured by serially connecting a switching element with one endconnected to the side of the power-supply voltage and another switchingelement with one end connected to ground. In this embodiment, an FET isused as a switching element. However, a switching element is not limitedto an FET. The first and the second wave-shaping sections 17A and 17Bare each formed of a coil. In the first wave-shaping section 17A, oneend is connected to a connecting point between the two FETs of the firstamplifier section 16A, and the other end is connected to the firstpower-supply electrodes 42A of the actuator body 4. In the secondwave-shaping section 17B, one end is connected to a connecting pointbetween the two FETs of the second amplifier section 16B, and the otherend is connected to the second power-supply electrodes 42B of theactuator body 4. Thus, the actuator body 4 is serially connected betweenthe coils and a half bridge.

The first and the second amplifier sections 16A and 16B each outputs asquare-wave voltage having a same (maximum) voltage value as thepower-supply voltage by switching between on and off states of the twoFETs. In addition, a low-pass filter is formed due to the capacity ofthe actuator body 4 and due to the inductances of the first and thesecond wave-shaping sections 17A and 17B, and then the square-wavevoltages output from the first and the second amplifier sections 16A and16B are reshaped into sinusoidal drive voltages, which are applied tothe actuator body 4. Note that it is preferable that the cut-offfrequency of the low-pass filter due to the inductances of the coils andthe capacity of the piezoelectric element be higher than the frequencyof the drive voltages (also referred to hereinafter as drivingfrequency) of the actuator body 4.

The drive power supply 11 adjusts the frequencies, phases, and effectivevalues of the first and the second drive voltages by controlling on/offoperation timings of the FETs of the first and the second amplifiersections 16A and 16B.

More specifically, the drive power supply 11 outputs the first and thesecond drive voltages having frequencies associated with the frequencyof the reference clock signal by performing on/off operation of the FETsof the first and the second amplifier sections 16A and 16B according tothe reference clock signal input from the clock generation section 14.That is, adjusting the frequency of the reference clock signal outputfrom the clock generation section 14 allows the frequencies of the firstand the second drive voltages to be adjusted.

In addition, the drive power supply 11 outputs the second drive voltagehaving a phase shift relative to the first drive voltage by shifting thephase of the reference clock signal input to the second amplifiersection 16B relative to that of the reference clock signal input to thefirst amplifier section 16A by the phase shift section 15, therebycausing on/off operation of the FETs of the second amplifier section 16Bto be performed at different times than those of the FETs of the firstamplifier section 16A. That is, adjusting the amount of the phase shiftperformed by the phase shift section 15 allows the phase differencebetween the first and the second drive voltages to be adjusted.

Furthermore, the drive power supply 11 changes the duty cycles (ratioseach of an On time relative to one period) of the square-wave voltagesto change the effective values of the first and the second drivevoltages by adjusting, in each of the first and the second amplifiersections 16A and 16B, the ratio between a time period during which oneFET of the two FETs is turned on and a time period during which theother FET is turned on according to the control signal from the controlsection 10. That is, adjusting the duty cycle of the square-wave voltagein each of the first and the second amplifier sections 16A and 16Ballows each of the effective values of the first and the second drivevoltages to be adjusted. Note that, in this embodiment, the drive powersupply 11 adjusts the duty cycles of the square-wave voltages in a rangeof 0%-50%.

Note that, although the description has been presented in terms of ahalf bridge of two channels generating the first and the second drivevoltages, the power supply circuit may be configured with a full bridgeof the two channels or an amplifier configuration.

In this regard, the first current detector 12A is serially connectedbetween the first wave-shaping section 17A and the first power-supplyelectrodes 42A of the actuator body 4. The second current detector 12Bis serially connected between the second wave-shaping section 17B andthe second power-supply electrodes 42B of the actuator body 4. Thesefirst and second power-supply electrodes 42A and 42B are formed ofresistors, and detect currents by voltage differences between the bothends. Thus, the first current detector 12A detects a current which flowsbetween the first power-supply electrodes 42A and the counter electrodes43 of the actuator body 4 depending on the first drive voltage (referredto hereinafter as first current), while the second current detector 12Bdetects a current which flows between the second power-supply electrodes42B and the counter electrodes 43 of the actuator body 4 depending onthe second drive voltage (referred to hereinafter as second current).However, since the efficiency of the ultrasonic actuator 2 in operationdecreases if a resistance value is too high, it is preferred that theresistance values of the first and the second current detectors 12A and12B be approximately 0.1-100Ω.

Furthermore, the position sensor 13 is disposed near the movable body 9.The position sensor 13 detects the position of the movable body 9, andoutputs position information thereof to the control section 10.

<<3: Operation of Drive Unit>>

<3.1: Basic Operation>

Operation of the ultrasonic actuator 2 will be described below. FIG. 8is a conceptual diagram illustrating a deviation in stretching vibrationof the first order according to this embodiment; FIG. 9 is a conceptualdiagram illustrating deviations in bending vibration of the secondorder; and FIGS. 10A-10D are conceptual diagrams illustrating a motionof the actuator body 4. Note that, in FIGS. 8-9 and 10A-10D, theprincipal faces of the actuator body 4 are parallel to the paper.

The electric wires 52 of the second flexible cable 7B are connected toground. The drive power supply 11 applies the first drive voltage of asinusoidal wave having a predetermined frequency to the firstpower-supply electrodes 42A on principal faces of the piezoelectricelement layers 41 through the electric wire 51A and the first externalpower-supply electrode 44A, and applies the second drive voltage of asinusoidal wave having almost the same amplitude and almost the samefrequency as those of the first drive voltage to the second power-supplyelectrodes 42B through the electric wire 51B and the second externalpower-supply electrode 44B.

Here, if the phase difference between the first and the second drivevoltages is 0°, stretching vibration of the first order is induced inthe actuator body 4 as shown in FIG. 8. Meanwhile, if the phasedifference is 180°, bending vibration of the second order is induced inthe actuator body 4 as shown in FIG. 9.

In addition, if the phase difference between the first drive voltageapplied to the first power-supply electrodes 42A and the second drivevoltage applied to the second power-supply electrodes 42B isapproximately 90° or −90°, stretching vibration of the first order andbending vibration of the second order are induced in a coordinatedmanner in the actuator body 4 as shown in FIGS. 10A-10D. This causes theshape of the actuator body 4 to change and vibrate sequentially as shownin FIGS. 10A-10D, and thus the driver elements 8 provided on theactuator body 4 each moves in an orbital path (specifically, a generallyelliptical path) as viewed in the direction into the paper of FIGS.10A-10D. That is, composite vibration of stretching vibration andbending vibration of the actuator body 4 causes the driver elements 8 tomove in elliptical paths. This elliptical movement causes the movablebody 9 contacted by the driver elements 8 to move relative to theactuator body 4.

In this regard, the actuator body 4 is arranged such that thelongitudinal direction of the principal faces thereof coincides with themovable direction of the movable body 9, and the lateral direction ofthe principal faces coincides with a direction in which the actuatorbody 4 is biased toward the movable body 9 by the support member 6B.That is, the expanding/contracting direction of stretching vibration ofthe actuator body 4 is the movable direction of the movable body 9, andthe vibratory direction of bending vibration is the direction in whichthe driver elements 8 press the movable body 9. Note that, the stackingdirection of the actuator body 4 is orthogonal to both theexpanding/contracting direction of stretching vibration and thevibratory direction of bending vibration. In addition, the longer sidefaces of the actuator body 4 are surfaces which intersect the directionof bending vibration (i.e., surfaces facing toward bending vibration).

As described previously, since the direction of stretching vibration ofthe actuator body 4 is coincident with the movable direction of themovable body 9, a larger amplitude of stretching vibration allows themovable body 9 to be moved over a longer distance. That is, the movablebody 9 can be moved faster with a same frequency. Meanwhile, sincebending vibration of the actuator body 4 occurs in the direction inwhich the driver elements 8 press the movable body 9, friction forcesbetween the movable body 9 and the driver elements 8 are affected bybending vibration. That is, if the movable body 9 is to be moved to theright as viewed in FIG. 2, the friction forces between the driverelements 8 and the movable body 9 are made high when the driver elements8 shift to the right, and the friction forces between the driverelements 8 and the movable body 9 are made low when the driver elements8 shift to the left.

As such, in this embodiment, the actuator body 4 is formed such that aresonant frequency of bending vibration of the second order isapproximately coincident with an anti-resonant frequency of stretchingvibration of the first order, and then the driving frequency of theactuator body 4 is set to a frequency near a resonant frequency ofbending vibration of the second order.

That is, driving the actuator body 4 at a frequency near a resonantfrequency of bending vibration allows the friction forces between themovable body 9 and the driver elements 8 to be increased, and thus themovable body 9 can be moved relatively through the friction forces. Inaddition, driving the actuator body 4 at a frequency near ananti-resonant frequency of stretching vibration prevents a high currentfrom flowing to the actuator body 4, and thus heat generation in theactuator body 4 can be prevented. Note that, since an impedance of theactuator body 4 at a resonant frequency of bending vibration is not aslow as an impedance at a resonant frequency of stretching vibration,there are no problems with a high current flowing to the actuator body 4at a resonant frequency of bending vibration.

As described previously, the drive unit 1 operates the ultrasonicactuator 2 and moves the movable body 9 to a desired position at adesired speed. Specifically, the drive unit 1 controls the moving speedand the position of the movable body 9 by adjusting the control signalto the drive power supply 11 according to a detect signal from theposition sensor 13. For example, the drive unit 1 adjusts the amount ofamplitude of the actuator body 4 by changing the reference frequency ofthe reference clock signal of the clock generation section 14, therebyadjusts the moving speed of the movable body 9. In this regard, since anamplitude change of stretching vibration associated with a change of thedriving frequency is more gradual in a frequency range near ananti-resonant frequency than in a frequency range near a resonantfrequency, adjustment of the moving speed of the movable body 9 bychanging the driving frequency can be stably performed by setting thedriving frequency to a frequency near an anti-resonant frequency ofstretching vibration as described previously.

Note that speed control can be also performed by control using thevoltage value of the drive voltage, or by setting the phase differencebetween the voltages applied to the first and the second power-supplyelectrodes to a value other than 90 degrees. In either case, since thespeed of the movable body is stabilized for the frequency by setting thedriving frequency to a frequency higher than an anti-resonant frequencyof stretching vibration, speed control can be stably performed even if aresonant frequency and an anti-resonant frequency of the actuator body4, the driving frequency, etc., vary.

<3.2: Voltage-Value Control of Drive Voltages>

Voltage-value control of the drive voltages of the drive unit 1 will bedescribed below.

In this embodiment, the drive unit 1 adjusts the voltage values of thefirst and the second drive voltages applied to the actuator body 4according to the value of current flowing to the actuator body 4. Thecontrol period of this voltage-value control is longer than the controlperiod of position control or speed control of the movable body 9. FIGS.11A-17B show the first and the second drive voltages and the first andthe second currents under various conditions.

For example, if the first and the second drive voltages V1 and V2 havinga same effective value of voltage, a same frequency, and differentphases as shown in FIGS. 11A and 12A are applied to a portion betweenthe first power-supply electrodes 42A and the counter electrodes 43 ofthe actuator body 4 (also referred to hereinafter as firstinter-electrode portion) and to a portion between the secondpower-supply electrodes 42B and the counter electrodes 43 (also referredto hereinafter as second inter-electrode portion), the first and thesecond currents A1 and A2 which have a same effective value of current,a same frequency, and different phases may flow respectively through thefirst and the second inter-electrode portions as shown in FIG. 11B, orthe first and the second currents A1 and A2 which have a same frequency,different phases, and different effective values of currents may flow asshown in FIG. 12B.

That is, since the actuator body 4 has a piezoelectric effect, the drivevoltage applied to one inter-electrode portion and the drive voltageapplied to the other inter-electrode portion have interaction with eachother. In addition, the ratio in the interaction may be non-uniform dueto asymmetry introduced in a manufacturing process of the actuator body4 and due to asymmetry of distribution of pressure applied to theactuator body 4 in driving operation. Therefore, even if drive voltageshaving a same effective value are applied to the first and the secondpower-supply electrodes 42A and 42B, the effective values of the firstand the second currents flowing therethrough may differ.

—Current Equalization Control—

Therefore, the drive unit 1 compares the first current A1 flowingthrough the first inter-electrode portion with the second current A2flowing through the second inter-electrode portion based on detectionresults of the first and the second current detectors 12A and 12B, andadjusts the voltages values of the first and the second drive voltagesV1 and V2 so that the difference between the current values of the firstand the second currents A1 and A2 is less than or equal to apredetermined threshold. Specifically, in the drive power supply 11, thecontrol section 10 adjusts the duty cycle of a square-wave voltage fromwhich the first and the second drive voltages V1 and V2 originate,thereby adjusts the effective values of the first and the second drivevoltages V1 and V2.

For example, if the effective value of the first current A1 is largerthan the effective value of the second current A2 as shown in FIG. 12B,the effective value of the first drive voltage V1 is adjusted to a lowervalue as shown in FIG. 13A, thereby adjusting the difference between theeffective values of the first and the second currents A1 and A2 to lessthan or equal to a predetermined threshold (see FIG. 13B). Specifically,the square-wave voltages output from the first and the second amplifiersections 16A and 16B are signals having a same amplitude, a samefrequency, a same duty cycle, and a phase shift before adjustment asshown in FIG. 18A. Note that, in FIGS. 18A-18B, the signals denoted with“1ch” are the square-wave voltages from the first amplifier section 16A,and the signals denoted with “2ch” are the square-wave voltages from thesecond amplifier section 16B. If the effective value of the first drivevoltage V1 is to be reduced, only the duty cycle of the square-wavevoltage is reduced while the amplitude, the frequency, and the phasedifference thereof are kept unchanged as shown in FIG. 18B. In doing so,the effective value of the first drive voltage V1 can be reduced.

Alternatively, the effective value of the second drive voltage V2 isadjusted to a higher value as shown in FIG. 14A, thereby adjusting thedifference between the effective values of the first and the secondcurrents A1 and A2 to less than or equal to a predetermined threshold(see FIG. 14B). In this regard, the difference between the effectivevalues of the first and the second currents A1 and A2 may be adjusted toless than or equal to a predetermined threshold by adjusting theeffective value of the first drive voltage V1 to a lower value and theeffective value of the second drive voltage V2 to a higher value.

In doing so, even if a difference arises between the first and thesecond currents A1 and A2, equalization of the first and the secondcurrents A1 and A2 can be pursued, thereby preventing a higher currentthan expected from flowing to the actuator body 4. As a result, heatgeneration in the actuator body 4 can be reduced, and the powerconsumption can also be reduced.

—Current Limitation Control—

In addition, the drive unit 1 may be configured such that equalizationof the first and the second currents is not performed, but instead thefirst and the second drive voltages V1 and V2 are controlled so thatneither the first nor the second current exceeds a predetermined upperlimit. That is, the drive unit 1 adjusts the voltage values of the firstand the second drive voltages V1 and V2 so that neither the first northe second current A1 nor A2 exceeds a predetermined upper limit basedon detection results of the first and the second current detectors 12Aand 12B. Specifically, in the drive power supply 11, the control section10 adjusts the duty cycle of a square-wave voltage from which the firstand the second drive voltages V1 and V2 originate, thereby adjusts theeffective values of the first and the second drive voltages V1 and V2.

For example, if the peak value of the first current A1 exceeds an upperlimit Amax as shown in FIG. 15B when the first and the second drivevoltages V1 and V2 having a same effective value of voltage, a samefrequency, and different phases as shown in FIG. 15A are applied to thefirst and the second inter-electrode portions of the actuator body 4,the effective value of the first drive voltage V1 is adjusted to a lowervalue as shown in FIG. 16A, thereby adjusting the peak value of thefirst current A1 to less than or equal to the upper limit Amax (see FIG.16B). Note that, the second drive voltage V2 is adjusted if the peakvalue of the second current A2 exceeds the upper limit Amax, and boththe first and the second drive voltages V1 and V2 are adjusted if boththe first and the second currents A1 and A2 exceed the upper limit Amax.

In doing so, the first and the second currents A1 and A2 can be reducedat most to less than or equal to the upper limit Amax, therebypreventing a higher current than expected from flowing to the actuatorbody 4. As a result, heat generation in the actuator body 4 can bereduced, and the power consumption can also be reduced.

Note that the drive voltages may be adjusted based on whether theeffective values of the first and the second currents A1 and A2 exceedan upper limit for the effective values or not, instead of whether thepeak values of the first and the second currents A1 and A2 exceed theupper limit Amax or not.

—Speed Priority Control—

Furthermore, if the driving speed of the movable body 9 has a higherpriority than the power consumption, the drive unit 1 adjusts thevoltage value of the drive voltage of the first or the secondinter-electrode portion, whichever is more electrically conductive, to ahigher value based on detection results of the first and the secondcurrent detectors 12A and 12B. More specifically, the drive voltage ofthe inter-electrode portion, of the first and the second inter-electrodeportions, through which a higher current value of current flows when thefirst and the second drive voltages V1 and V2 having a same voltagevalue are applied is adjusted to a higher value.

For example, if the first current A1 is greater than the second currentA2 when the first and the second drive voltages V1 and V2 having a sameeffective value of voltage, a same frequency, and different phases asshown in FIG. 12A are applied to the first and the secondinter-electrode portions of the actuator body 4, the firstinter-electrode portion is more electrically conductive than the secondinter-electrode portion. Thus the voltage value of the first drivevoltage V1 is adjusted to a higher value (e.g., to a configurable upperlimit) as shown in FIG. 17A, thereby adjusting the first current A1 toan even higher value. Note that, if the second current A2 is greater,the second drive voltage V2 is adjusted to a higher value.

That is, one of the first and the second inter-electrode portions ismore conductive than the other due to interaction therebetween. In orderto increase a driving speed, both the first and the second drivevoltages may be adjusted to higher values, but increasing the drivingvoltage applied to the less conductive inter-electrode portion is not anefficient way. Therefore, as described above, adjusting the drivevoltage corresponding to the more electrically conductive one to ahigher value allows the driving speed to be efficiently increased.However, from a viewpoint of heat generation in the actuator body 4 andpower consumption, it is preferable that the drive voltage be set to ahigher value only for a certain limited period of time, for example, apredetermined period during which heat generation in the actuator body 4is acceptable etc., and that the drive voltage be returned to anoriginal value when the certain period of time has elapsed.

—Variations—

Whereas, in the aforementioned controls, the drive unit 1 controls thefirst and the second drive voltages based on the detection results ofthe first and the second current detectors 12A and 12B, the method isnot limited to this. For example, the drive unit 1 may store the firstand the second currents which had been measured in advance beforeshipment etc. or the first and the second drive voltages calculated fromthe first and the second currents measured in advance in a memorysection 18 which is connected to the control section 10 so that signalscan be transmitted and received therebetween. Moreover, the drive unit 1may read the stored data from the memory section 18 when actuallyoperating the ultrasonic actuator 2, and set the first and the seconddrive voltages based on the data to provide the aforementioned controls.

In addition, instead of storing the first and the second currents uponshipment etc., the drive unit 1 may be configured such that thedetection results of the first and the second current detectors 12A and12B, or the first and the second drive voltages calculated from thedetection results may be stored (i.e., learnt) at required timings whileactually operating the ultrasonic actuator 2. For example, in a case ofthe aforementioned current equalization control, if the differencebetween the current values of the first and the second currents exceedsa predetermined threshold during operation of the ultrasonic actuator 2,the drive unit 1 may adjust the first and the second drive voltages sothat the difference falls to or below the threshold, and after thisadjustment, store the first and the second drive voltages in the memorysection 18, and then use the stored first and second drive voltages whenoperating afterward. In addition, even when the stored first and seconddrive voltages are used, the drive unit 1 may monitor the first and thesecond currents, adjust again the first and the second drive voltages ifthe difference between the current values of the first and the secondcurrents exceeds the predetermined threshold, then update the storedvoltage values in the memory section 18 accordingly.

Advantages of Embodiment

Therefore, according to this embodiment, the actuator body 4 can beoperated at drive voltages depending on the first and the secondcurrents by adjusting the first and the second drive voltages so thatthe voltage values are different from each other, and thus heatgeneration in the actuator body 4 can be reduced, and the powerconsumption can also be reduced.

Specifically, if the difference between the current values of the firstand the second currents exceeds a predetermined value, adjusting thevoltage values of the first and the second drive voltages so that thedifference falls to or below the predetermined value prevents a highcurrent from flowing to the actuator body 4, and thus heat generation inthe actuator body 4 can be reduced, and the power consumption can alsobe reduced.

In addition, even if the first and the second currents are notequalized, the drive voltage corresponding to either the first or thesecond current, which exceeds an upper limit is adjusted to a lowervalue so that both the first and the second currents are adjusted toless than or equal to the upper limit, and thus heat generation in theactuator body 4 can be reduced, and the power consumption can also bereduced.

Furthermore, if the driving speed has a higher priority than the powerconsumption, further increasing the drive voltage corresponding toeither the first or the second current, whichever has a higher currentvalue, allows high current to efficiently flow to the actuator body 4,and thus the driving speed can be efficiently increased.

Other Embodiments

With respect to the previous embodiment, the following configurationsmay also be used.

Whereas, in the previous embodiment, the effective values of the firstand the second drive voltages are changed by changing the duty cycles ofthe square-wave voltages, the method is not limited to this. Forexample, the drive unit may be configured such that the voltage valuesof the first and the second drive voltages are changed by changing thepower-supply voltage by a DC-DC converter.

In addition, the first and the second current detectors 12A and 12B maybe connected between the counter electrodes 43 and ground. In such acase, a current value can be determined only with a potential of oneside. Alternatively, the first and the second current detectors 12A and12B may be respectively connected between the first and the secondamplifier sections 16A and 16B and the first and the second wave-shapingsections 17A and 17B. In such a case, a current value can be determinedwith the power-supply voltage and the potential on the side of thewave-shaping section of the resistor. In addition, since the first andthe second current detectors 12A and 12B configured with resistors alsofunction as protective resistors for the actuator body 4, sudden heatgeneration in the actuator body 4 can be prevented even if the actuatorbody 4 or other members short out. Note that, whereas the first and thesecond current detectors 12A and 12B are configured with resistors, theconfiguration is not limited to this; any configuration such as acurrent transformer, a hall element, etc., may be used as far as currentcan be detected with that configuration.

Moreover, whereas, in this embodiment, the first and the second drivevoltages are adjusted based on the effective values of the first and thesecond currents flowing through the first and the second inter-electrodeportions, the first and the second drive voltages may be adjusted basedon, in addition to the first and the second currents, the activecurrents of the first and the second inter-electrode portionsrespectively taking into consideration the phases of the first and thesecond drive voltages.

In this regard, since the output of the ultrasonic actuator 2 maydecrease if the drive voltages remain in a condition in which the drivevoltages have been adjusted as described previously, it is preferablethat the drive voltages be returned to a condition before the adjustmentif the current values have fallen below a predetermined threshold for apredetermined period of time. In this case, the drive voltages are notreturned to the condition before the adjustment all at once, but thedrive voltages are gradually returned in a stepwise fashion, and thedrive voltages are adjusted again if the current values exceed apredetermined threshold during a returning process. It is preferablethat the predetermined period of time be set to a longer value than thecontrol period of speed control; for example, if the control period ofspeed control is 10 μs-5 ms, it is preferable to set the predeterminedperiod to 10 ms-10 s.

Furthermore, the shape of the driver elements 8 is not limited to acylinder. It may be a sphere or a quadrangular prism. If the driverelements 8 are spherical in shape, this is preferable because the driverelements 8 and the actuator body 4 are made contact and fixed in pointcontact.

The electrical connection members are not limited to flexible cables.For example, wires, contact pins, conductive rubber, etc., may be used.In addition, whereas the configuration of connection using ananisotropic conductive adhesive film has been described, other electricconnection methods, such as connection by a low melting-point metal (asolder, etc.), connection by wire bonding, connection by anon-anisotropic conductive adhesive film, connection by a conductiveadhesive agent (a liquid adhesive agent, etc.), connection by crimping,etc., may be used. Conductive rubber has, for example, a stackingconfiguration formed of support layers made primarily of silicone rubberand conductive layers in which silicone rubber and particles of metalsuch as silver are mixed, and is electrically insulated in the stackingdirection, and thus anisotropic. One piece of conductive rubber may beprovided or two pieces of conductive rubber may be provided on one sideface of the actuator body. If conductive rubber is used, conductiverubber members may be used as the support members 6A and 6C. If onepiece of conductive rubber is provided on one side face of the actuatorbody, it is preferable that electrical insulation between the externalpower-supply electrode 44 and the external counter electrode 45,electrical insulation between the first and the second externalpower-supply electrodes 44A and 44B, and electrical insulation betweenthe two external counter electrodes 45 be provided using the insulatingproperties of the conductive rubber in the stacking direction. In such acase, each conductive layer functions as one of the first power-supplyconductive member, the second power-supply conductive member, or thecounter conductive members.

The first and the second connection electrodes J1 and J2 arerespectively provided in center portions in the longitudinal directionof the corresponding principal faces of the corresponding piezoelectricelement layers 41, and have a shape extending in a direction generallyparallel to the short sides of the principal faces of the piezoelectricelement layers 41; more preferably, in the direction along the longsides of the piezoelectric element layers 41, it is preferable that thewidths of the first and the second connection electrodes J1 and J2 beapproximately 5%-40% of the length in the direction along the long sidesof the piezoelectric element layers 41. This is because too largeelectrode areas will impede bending vibration of the second-order modeeven though higher-amplitude stretching vibration occurs as theelectrode areas of the first and the second connection electrodes J1 andJ2 increase. Meanwhile, the first and the second connection electrodesJ1 and J2 are ideally formed over almost the entire range in thedirection along the short sides of the piezoelectric element layers 41,but forming the first and the second connection electrodes J1 and J2 soas to reach edge portions in the lateral direction of the correspondingpiezoelectric element layers 41 makes it difficult to provide insulationbetween the internal electrode layers. Therefore, it is preferable thatthe first and the second connection electrodes J1 and J2 be formed inregions other than both edge portions in the direction along the shortsides of the corresponding principal faces of the correspondingpiezoelectric element layers 41. Specifically, it is preferable that thefirst and the second connection electrodes J1 and J2 be formed over mostof the regions other than regions from either edge in the directionalong the short sides of the corresponding principal faces of thecorresponding piezoelectric element layers 41 to a distance of thelength in the thickness direction of the piezoelectric element layers 41toward the centers in the direction along the short sides.

Although the number of the power-supply electrodes 42 in the firstpattern and the number of the power-supply electrodes 42 in the secondpattern do not necessarily need to be the same, it is preferable thatthe numbers be the same. Although the power-supply electrodes 42 in thefirst pattern and the power-supply electrodes 42 in the second patterndo not necessarily need to be disposed alternately, it is preferable tobe disposed alternately. This is because symmetric nature of vibrationof the actuator body 4 will improve. This is also because unnecessaryvibration will not occur in the actuator body 4, and thus energy losswill be significantly reduced.

Although the electrodes may be formed on principal faces of the actuatorbody 4, it is preferable that the electrodes not be formed on anyprincipal faces of the actuator body 4. This is because, by not formingthe electrodes on any principal faces, which have a largest area of theouter faces of the actuator body 4, a short circuit is less likely tooccur even if an electrode contacts a metal part in the vicinitythereof.

Whereas, in the previous embodiment, the movable body 9, to which adriving force of the ultrasonic actuator 2 is applied to drive, has aplate-like shape, the configuration is not limited to this, but anyconfiguration may be used as the configuration of the movable body 9.For example, as shown in FIG. 19, the movable body may be a disk 9rotatable about a predetermined axis X, and may be configured such thatthe driver elements 8 of the ultrasonic actuator 2 contact a peripheralside surface 9 a of the disk 9. In a case of such a configuration, thedisk 9 is caused to rotate about the predetermined axis X by generallyelliptical movements of the driver elements 8 when the ultrasonicactuator 2 is operated. Alternatively, the ultrasonic actuator 2 may beconfigured so as to be attached to the movable body, with the driverelements 8 in contact with a fixed body, and to move together with themovable body 9.

Whereas, in the previous embodiment, the support is configured by thecase 5, the support may be configured by anything.

It is preferable that the region where the power-supply electrodes 42and the counter electrodes 43 do not overlap as viewed in the stackingdirection be a region from either edge in the longitudinal direction ofthe piezoelectric element layers 41 to a distance more than or equal to10% of the length in the longitudinal direction of the piezoelectricelement layers 41 toward the center in the longitudinal direction. It ismore preferable that the region where the power-supply electrodes 42 andthe counter electrodes 43 do not overlap as viewed in the stackingdirection be a region from either edge in the longitudinal direction ofthe piezoelectric element layers 41 to a distance more than or equal to20% of the length in the longitudinal direction of the piezoelectricelement layers 41 toward the center in the longitudinal direction. Thisis because little stress is generated in the vicinity of each edge inthe longitudinal direction of the piezoelectric element layers 41 duringstretching vibration of the first-order mode. This is also because aneffect on connecting portions between the side faces of thepiezoelectric element and the electrical connection members can bereduced.

Whereas, in the previous embodiment, an example has been presented inwhich the voltage applied to the second power-supply electrodes 42B hasa phase shift of approximately +90° or −90° relative to the voltageapplied to the first power-supply electrodes 42A, the configuration isnot limited to this, but other phase shifts may be applied. In addition,a voltage may be selectively applied to only either the firstpower-supply electrodes 42A or the second power-supply electrodes 42B.

Whereas, in the previous embodiment, the ultrasonic actuator 2 issupported using the support members 6A, 6B, and 6C, the method is notlimited to this method. For example, as shown in FIG. 20, only thesupport member 6B may be provided on the end face on which the driverelements are not provided, of the two end faces of the piezoelectricelement. The support member 6B regulates movement of the actuator body 4in the driving direction (direction along the long sides of theprincipal faces), and allows the actuator body 4 to move in a directionin which the driver elements 8 make contact with the movable body 9(direction along the short sides of the principal faces). In addition,the support member 6B generates a pressing force in a direction in whichthe driver elements 8 make contact with the movable body 9, therebyincreasing the friction forces between the driver elements 8 and themovable body 9.

Although the actuator body 4, including the piezoelectric elementlayers, has been described as itself producing stretching vibration andbending vibration in a coordinated manner, a configuration in which apiezoelectric body or the actuator body 4 is attached to a substratemade of metal etc., or a configuration in which a piezoelectric body orthe actuator body 4 is interposed in a resonator made of metal etc. mayalso provide similar advantages. In such cases, the resonator configuredincluding the piezoelectric body constitutes the actuator body, and theresonator is disposed in a case with a compressive force applied inadvance.

Although the driver elements 8 have been described as fixed on a longerside face of the actuator body 4, the driver elements 8 may be fixed ona shorter side face.

Although the stretching vibration has been described as of the firstorder and the bending vibration has been described as of the secondorder, they may be resonant vibrations of other orders.

It is to be understood that the foregoing embodiments are illustrativein nature, and are not intended to limit the scope of the invention,application of the invention, or use of the invention. The describedembodiments are to be considered in all respects only as illustrated andnot restrictive. The scope of the invention is, therefore, indicated bythe appended claims rather than by the foregoing description. Allvariations and changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

Examples

Specific examples of adjusting two-phase drive voltages in theultrasonic actuator 2 will be described below.

Referring as one set to a structure stacked in the order of apiezoelectric element layer 41 on which a power-supply electrode 42 inthe first pattern is provided, a piezoelectric element layer 41 on whicha counter electrode 43 is provided, a piezoelectric element layer 41 onwhich a power-supply electrode 42 in the second pattern is provided, anda piezoelectric element layer 41 on which a counter electrode 43 isprovided, the actuator body 4 includes five sets, where, of theoutermost two piezoelectric element layers 41, the piezoelectric elementlayer 41 on which an electrode 42 (or 43) is exposed to the ambient hasanother piezoelectric element layer 41 on which no electrodes areprovided stacked thereon. In this way, twenty-one piezoelectric elementlayers 41 are stacked interposing power-supply electrodes 42 or counterelectrodes 43. The piezoelectric element layers 41 are made of leadzirconate titanate. The dimensions of the actuator body 4 having such aconfiguration is 6.0 mm long (dimension in the longitudinal direction),1.7 mm wide (dimension in the lateral direction), and 2.0 mm thick(dimension in the thickness direction).

Drive voltages of various voltage patterns as shown below were appliedto this actuator body 4.

Tables 1-5 respectively show the parameter values of the first and thesecond drive voltages V1 and V2 according to the voltage patterns 1-5,as well as the currents flowing to the actuator body 4 and the speed ofthe movable body 9 associated therewith.

TABLE 1 1ch 2ch Phase Difference — 90° Driving Frequency 280 kHz 280 kHzVoltage Value 4 V 4 V Current Value 0.050 A 0.049 A Driving Speed 22mm/s

More specifically, in the voltage pattern 1 shown in Table 1, the phasedifference between the first and the second drive voltages V1 and V2 is90°, the frequencies of the first and the second drive voltages V1 andV2 are both 280 kHz, and the effective values of the voltages are both 4V. Under this condition, the effective value of the first current A1flowing through the first inter-electrode portion of the actuator body 4depending on the first drive voltage V1 was 0.050 A, and the effectivevalue of the second current A2 flowing through the secondinter-electrode portion of the actuator body 4 depending on the seconddrive voltage V2 was 0.049 A. The speed of the movable body 9 under thiscondition was 22 mm/s.

In the voltage pattern 2 shown in Table 2, the frequencies of the firstand the second drive voltages V1 and V2 are different from those of thevoltage pattern 1.

TABLE 2 1ch 2ch Phase Difference — 90° Driving Frequency 275 kHz 275 kHzVoltage Value 4 V 4 V Current Value 0.101 A 0.085 A Driving Speed 51mm/s

More specifically, the frequencies of the first and the second drivevoltages V1 and V2 are both 275 kHz. Under this condition, the effectivevalue of the first current A1 was 0.101 A, and the effective value ofthe second current A2 was 0.085 A. The speed of the movable body 9 underthis condition was 51 mm/s. In this way, as the parameter values(driving frequencies, in this example) of the first and the second drivevoltages change, a proportion between the first and the second currentsA1 and A2 also varies.

Thus, the voltage values of the first and the second drive voltages V1and V2 were adjusted as the voltage pattern 3 shown in Table 3.

TABLE 3 1ch 2ch Phase Difference — 90° Driving Frequency 275 kHz 275 kHzVoltage Value 3.4 V 4 V Current Value 0.085 A 0.085 A Driving Speed 50mm/s

More specifically, the effective value of the first drive voltage V1 was3.4 V. The other conditions were the same as those of the voltagepattern 2. The result was that the effective value of the first currentA1 corresponding to the first drive voltage V1 was 0.085 A, and theeffective value of the second current A2 corresponding to the seconddrive voltage V2 was 0.085 A. The speed of the movable body 9 under thiscondition was 50 mm/s. In this way, reducing the effective value of thedrive voltage corresponding to the higher current causes the differencebetween the current values of the first and the second currents A1 andA2 to decrease, thus equalization of both currents can be pursued.

Alternatively, adjustment may be performed so as to increase the voltagevalue of the drive voltage corresponding to the lower current as thevoltage pattern 4 shown in Table 4.

TABLE 4 1ch 2ch Phase Difference — 90° Driving Frequency 275 kHz 275 kHzVoltage Value 4 V 4.6 V Current Value 0.101 A 0.102 A Driving Speed 58mm/s

More specifically, the effective value of the second drive voltage V2was 4.6 V. The other conditions were the same as those of the voltagepattern 2. The result was that the effective value of the first currentA1 corresponding to the first drive voltage V1 was 0.101 A, and theeffective value of the second current A2 corresponding to the seconddrive voltage V2 was 0.102 A. The speed of the movable body 9 under thiscondition was 58 mm/s. In this way, increasing the effective value ofthe drive voltage corresponding to the lower current causes thedifference between the current values of the first and the secondcurrents A1 and A2 to decrease, thus equalization of both currents canbe pursued.

Moreover, depending on the conditions of the first and the second drivevoltages, the first and the second currents may exceed a predeterminedupper limit as the voltage pattern 5 shown in Table 5. In such a case,even though the first and the second currents are not equalized, thedrive voltages are adjusted so that the first and the second currentsare less than or equal to the upper limit as the voltage pattern 6 shownin Table 6.

TABLE 5 1ch 2ch Phase Difference — 90° Driving Frequency 275 kHz 275 kHzVoltage Value 10 V 10 V Current Value 0.130 A 0.105 A Driving Speed 85mm/s

More specifically, first, the effective values of the first and thesecond drive voltages V1 and V2 were both 10 V. The other conditionswere the same as those of the voltage pattern 2. The result was that theeffective value of the first current A1 corresponding to the first drivevoltage V1 was 0.130 A, and the effective value of the second current A2corresponding to the second drive voltage V2 was 0.105 A. The speed ofthe movable body 9 under this condition was 85 mm/s. Here, the upperlimit of the effective values of the first and the second currents is0.120 A.

TABLE 6 1ch 2ch Phase Difference — 90° Driving Frequency 275 kHz 275 kHzVoltage Value 9.5 V 10 V Current Value 0.120 A 0.105 A Driving Speed   84 mm/s Limit Voltage 0.120 A

Therefore, the effective value of the first drive voltage V1 was changedto 9.5 V. The other conditions were unchanged. The result was that theeffective value of the first current A1 corresponding to the first drivevoltage V1 was 0.120 A, which was the upper limit, and the effectivevalue of the second current A2 corresponding to the second drive voltageV2 was 0.105 A. The speed of the movable body 9 under this condition was84 mm/s. In this way, reducing the effective value of the drive voltagecorresponding to a current whose effective value exceeds the upperlimit, of the first and the second currents A1 and A2, prevents thefirst and the second currents A1 and A2 from exceeding the upper limit,and thus allows reduced power consumption.

Furthermore, if a higher priority needs to be given to the driving speedof the movable body 9 than to power consumption, the driving voltage ofthe inter-electrode portion having a higher conductivity, of the firstand the second inter-electrode portions, is increased temporarily.

TABLE 7 1ch 2ch Phase Difference — 90° Driving Frequency 275 kHz 275 kHzVoltage Value 5 V 4 V Current Value 0.120 A 0.087 A Driving Speed 70mm/s

More specifically, since the result of the voltage pattern 2 revealsthat the first inter-electrode portion, to which the first drive voltageV1 is applied, is more electrically conductive, the effective value ofthe first drive voltage V1 was set to 5 V in the voltage pattern 6. Theother conditions were the same as those of the voltage pattern 2. Theresult was that the effective value of the first current A1corresponding to the first drive voltage V1 was 0.120 A, which was theupper limit of acceptable currents, and the effective value of thesecond current A2 corresponding to the second drive voltage V2 was 0.087A. In this way, even though the difference between the first and thesecond currents A1 and A2 widened, the speed of the movable body 9significantly increased to 70 mm/s. That is, increasing the drivevoltage applied to the more conductive inter-electrode portion allowsthe speed of the movable body 9 to be efficiently increased.

It is to be understood that the invention is not limited to thedisclosed examples, but on the contrary, may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristic thereof. Thus, the described embodiments are to beconsidered in all respects only as illustrated and not restrictive. Thescope of the invention is, therefore, indicated by the appended claimsrather than by the foregoing description. All variations and changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

The invention claimed is:
 1. A drive unit, comprising: a vibratoryactuator having an actuator body and configured to output a drivingforce by inducing vibration in the actuator body, the actuator bodyincluding a piezoelectric element in a substantially rectangular shapeand an electrode layer having first power-supply electrodes and secondpower-supply electrodes on a substantially rectangular face of thepiezoelectric element, the first power-supply electrodes arranged in oneof two diagonal directions of the substantially rectangular face, andthe second power-supply electrodes arranged in the other of the twodiagonal directions of the substantially rectangular face, and a controlsection configured to induce the vibration in the actuator body byapplying a first and a second AC voltages having a same frequency anddifferent phases to the electrode layer, the first AC voltage applied tothe first power-supply electrodes, and the second AC voltage applied tothe second power-supply electrodes, wherein the control section adjuststhe first AC voltage and the second AC voltage so that the first ACvoltage and the second AC voltage have different effective values fromeach other, and an effective value of a first AC current flowing inresponse to the first AC voltage is different from an effective value ofa second AC current flowing in response to the second AC voltage.
 2. Adrive unit, comprising: a vibratory actuator having an actuator body andconfigured to output a driving force by inducing vibration in theactuator body, the actuator body including a piezoelectric element in asubstantially rectangular shape and an electrode layer having firstpower-supply electrodes and second power-supply electrodes on asubstantially rectangular face of the piezoelectric element, the firstpower-supply electrodes arranged in one of two diagonal directions ofthe substantially rectangular face, and the second power-supplyelectrodes arranged in the other of the two diagonal directions of thesubstantially rectangular face, and a control section configured toinduce the vibration in the actuator body by applying a first and asecond AC voltages to the electrode layer, the first AC voltage appliedto the first power-supply electrodes, and the second AC voltage appliedto the second power-supply electrodes, where a frequency of the first ACvoltage is equal to a frequency of the second AC voltage, wherein thecontrol section adjusts the frequencies of the first and second ACvoltages with the frequencies kept equal to each other, andindependently adjusts effective values of the first and second ACvoltages in accordance with the frequencies.
 3. The drive unit of claim2, wherein the control section adjusts the effective values of the firstAC voltage and the second AC voltage so that the effective values aredifferent from each other in accordance with the frequencies of thefirst and second AC voltages.
 4. A drive unit, comprising: a vibratoryactuator having an actuator body and configured to output a drivingforce by inducing vibration in the actuator body, the actuator bodyincluding a piezoelectric element in a substantially rectangular shapeand an electrode layer having first power-supply electrodes and secondpower-supply electrodes on a substantially rectangular face of thepiezoelectric element, the first power-supply electrodes arranged in oneof two diagonal directions of the substantially rectangular face, andthe second power-supply electrodes arranged in the other of the twodiagonal directions of the substantially rectangular face, and a controlsection configured to induce the vibration in the actuator body byapplying a first and a second AC voltages to the electrode layer, thefirst AC voltage applied to the first power-supply electrodes, and thesecond AC voltage applied to the second power-supply electrodes, where afrequency of the first AC voltage is equal to a frequency of the secondAC voltage, wherein the control section adjusts the frequencies of thefirst and second AC voltages, and a difference between an effectivevalue of the first AC voltage and an effective value of the second ACvoltage changes in accordance with the frequencies of the first andsecond AC voltages.